Thermosetting epoxy resin compositions and thermosets therefrom

ABSTRACT

Described are novel thermosetting epoxy resin compositions suitable for making cured resins, prepregs and stiff, tough thermoset composites. The thermosetting compositions comprise a polyepoxide component, an amine hardner and a specified amount of certain aromatic oligomers containing functional groups which are reactive with the polyepoxide and/or hardener under curing conditions for the composition. The cured resins have a multiphase morphology which comprises at least one glassy continuous phase and at least one glassy discontinuous phase and have a fracture toughness, K IC , of at least 1.0 MPam 1/2 .

This application is a division of application Ser. No. 724,133 filed4-16-85 now U.S. Pat. No. 4,656,208, which is a continuation-in-part ofapplication Ser. No. 702,518 filed Feb. 19, 1985.

This invention relates to thermosetting epoxy resin compositions, andmore particularly to resin modified thermosetting epoxy resincompositions which cure into thermosets having a multiphase morphologythat makes them extremely tough and stiff.

BACKGROUND OF THE INVENTION

Epoxy resins are well known for use in making advanced or highperformance composites comprising high strength fiber made of glass,boron, carbon or the like. Structures made of these composites can weighconsiderably less than their metal counterparts at equivalent strengthand stiffness. Higher modulus epoxy composites, however, have beenrelatively brittle. This brittleness restricts their wider applicationbecause, for example, damage tolerance, an important property of flightcritical components in aircraft, is related to brittleness of thecomponent.

One approach in making epoxy composites tougher has been to introducefunctionally terminated rubbery polymers into the epoxy resinformulations. The thermosets resulting from these formulations, whilehaving increased toughness, have reduced modulus.

Another approach has been to incorporate engineering thermoplastics intothe epoxy resin formulation. Various thermoplastics have been suggestedand the use of a polyethersulfone as the thermoplastic modifier forepoxy resin formulations was studied by C. B. Bucknall et al and isdiscussed in the British Polymer Journal, Vol. 15, March 1983 at pages71 to 75. Bucknall et al's studies were carried out on curedepoxy-polyethersulfone blends prepared from trifunctional and/ortetrafunctional aromatic epoxides, diaminodiphenylsulfone ordicyandiamide hardener and various amounts of Victrex 100P manufacturedby ICI Ltd., said to be a relatively low molecular weight grade ofpolyethersulfone. The studies showed that phase separation occurred incertain of the cured epoxy-polyethersulfone blends and that some of thecured blends exhibited distinct nodular morphological features. Analysesindicated that the polyethersulfone was concentrated in the nodules andBucknall et al surmised that the nodules were not formed bypolyethersulfone alone but by a crosslinked epoxypolyethersulfonecopolymer. Bucknall et al found no clear correlation between compositionand mechanical properties such as elastic modulus, fracture toughnessand creep of the cured blends and concluded that the addition of thepolyethersulfone had little effect on the fracture toughness of theresin mixtures, irrespective of the degree of phase separation or themorphology.

Yet another approach for improving the mechanical properties of curedepoxy resins is described in U.S. Pat. No. 4,330,659 to King et al. Kinget al disclose using as the hardener for epoxy resins the reactionproduct of diaminodiphenylsulfone with diglycidyl ethers of polyhydricphenols. The cured resins prepared from mixtures of a "modified"hardener obtained by adducting the coreaction product of the diglycidylether of bisphenol A and additional bisphenol A withdiaminodiphenylsulfone, and tetraglycidylated methylene dianiline arereported to have increased impact strength and toughness as comparedwith the cured resins obtained using unmodified diaminodiphenylsulfoneas the hardener.

SUMMARY OF THE INVENTION

Now, in accordance with this invention it has been found that certainthermosetting epoxy resin compositions provide tough epoxy thermosetswhich are characterized by a multiphase morphology consisting of atleast one glassy continuous phase and at least one glassy discontinuousphase. The superior toughness advantage realized with the thermosets ofthis invention is achieved without detriment to other desirableproperties associated with epoxy thermosets.

Accordingly, the present invention relates to a thermosetting epoxyresin composition comprising (a) a polyepoxide component having onaverage more than one epoxide group per molecule and a glass transitiontemperature below about 50° C., (b) an amount of an amine hardenersufficient to provide from 0.8 to 1.5 equivalent of active hydrogenatoms per one equivalent of epoxide groups in the composition and (c)from 20 to 50% by weight of the composition of an aromatic oligomerhaving a number average molecular weight between about 2,000 and about10,000, a glass transition temperature between about 125° C. and 250° C.and at least 1.4 functional groups which are reactive with (a) or (b),or (a) and (b) under curing conditions for the composition. Theinvention also relates to thermosets of the crosslinked epoxy resincomposition, to prepregs comprising the epoxy resin composition and highstrength filaments or fibers and to composites comprising thecrosslinked epoxy composition and high strength filaments or fibers.

BRIEF DESCRIPTION OF THE DRAWING

The invention is further illustrated in the Figures in which FIGS. 1 to4 are photomicrographs of RuO₄ -stained microtomed sections of thethermoset matrices of Example 10, Part B and Examples 11 to 13,respectively.

FIGS. 5(a) and 5(b) illustrate the test specimens used in determiningfracture energy (G_(IC)) and fracture toughness (K_(IC)) of thermosetsof this invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The thermosetting epoxy resin compositions of this invention comprise(a) a polyepoxide component having a glass transition temperature belowabout 50° C.; (b) an amine hardener; and (c) an aromatic oligomer thatis reactive with (a) or (b) or (a) and (b), has a molecular weight(number average) between about 2000 and 10,000, and a glass transitiontemperature between about 125° C. and 250° C.

The polyepoxide component contains on average more than one epoxidegroup Per molecule and preferably at least 2 epoxide groups permolecule. The term epoxide group as used herein refers to the simplestepoxide group which is the three-membered ring, ##STR1## The terms ofα-epoxy (or epoxide), 1,2-epoxy (or epoxide), vicinal epoxy (or epoxide)and oxirane group are also art recognized terms for this epoxide group.Polyepoxide compounds having between 2 and about 4 epoxide groups permolecule and a glass transition temperature below 20° C. areparticularly preferred. Suitable aromatic polyepoxide compounds areresorcinol diglycidyl ether (or 1,3-bis-(2,3-epoxypropoxy)benzene)marketed, for example, by Wilmington Chemical as HELOXY® 69; diglycidylether of bisphenol A (or 2,2-bis[p-(2,3-epoxypropoxy)phenyl]propane);triglycidyl p-aminophenol (or4-(2,3-epoxypropoxy)-N,N-bis(2,3-epoxypropyl)aniline); diglycidyl etherof bromobisphenol A (or2,2-bis[4-(2,3-epoxypropoxy)3-bromophenyl]propane; diglycidylether ofbisphenol F (or 2,2-bis[p-(2,3-epoxypropoxy)phenyl]methane); triglycidylether of meta-aminophenol (or 3-(2,3-epoxypropoxy)N,N-bis(2,3-epoxypropyl)aniline); and tetraglycidyl methylene dianiline(or N,N,N',N'-tetra(2,3-epoxypropyl) 4,4'diaminodiphenyl methane).Combinations of two or more polyepoxide compounds can be used as thepolyepoxide component. Preferred combinations include mixtures ofresorcinol diglycidyl ether and the triglycidylaminophenols ortetraglycidyl methylene dianiline, and mixtures of thetriglycidyaminophenols and the diglycidyl ether of butanediol (or1,4-bis[2,3-epoxypropoxy]butane) or the diglycidyl ethers ofpolypropylene glycol, particularly trior tetra-(α-propylene glycol)di-(2,3-epoxypropyl) ether. Particularly preferred are polyepoxidecomponents which comprise aromatic polyepoxide compounds and up to about50% of one or more aromatic or aliphatic diepoxide compounds, and whichhave glass transition temperatures between about -100° C. and about 20°C.

The aromatic oligomer, as stated, contains functional groups which arereactive with the polyepoxide component and/or the amine hardener of thecomposition. In one preferred embodiment the oligomer is epoxy-reactive(i.e. reacts with epoxide groups) and has at least 1.4 epoxyreactivegroups per molecule. In another embodiment the oligomer isepoxy-functional, i.e. it contains epoxide groups. The reactive aromaticoligomer preferably contains divalent aromatic groups such as phenylene,diphenylene or naphthalene groups linked by the same or differentdivalent non-aromatic linking groups. Exemplary linking groups areoxy(--O--); sulfonyl(--SO₂ --); oxyalkylene or oxyalkyleneoxy(--OR-- or--ORO-- wherein R is lower alkylene preferably with 1-3 carbon atoms);lower alkylene or alkylidene (R-- or --R(R₁)_(y) wherein R and R₁ areindependently lower alkylene and y is 1 or 2); ester groups such as--(R₁)_(x) COO(R₂)_(y) -- wherein R₁ and R₂ are independently loweralkylene preferably with 1 to 3 carbons and x and y are independentlyzero or 1; and oxoalkylene ##STR2## where R₁ and R₂ are independentlylower alkylene where x and y are independently zero or 1. The aromaticunits can be substituted with non-interferring substituents such aschlorine, lower alkyl, phenyl etc. Generally, at least twenty-fivepercent of the total number of carbon atoms in the reactive aromaticoligomer will be in aromatic structures, and preferably at least about50% of the total carbon atoms are in aromatic structures.

The preferred reactive aromatic oligomers are polyethers, polysulfonesor polyethersulfones and more preferably contain sulfone bridgeddiphenylene units or ketone bridged diphenylene units. Other types ofunits which can be present in these preferred oligomers are aromatic orcycloaliphatic units that are not bridged (e.g., naphthalene) or arebridged by groups which are essentially nonpolar, examples of which arealkylidene such as isopropylidene bridges.

The reactive aromatic oligomers preferably have reactive groups that areterminal groups on the oligomer backbone and more preferably arereactive groups at the ends of oligomeric backbones which have little orno branching. The preferred reactive groups of the reactive aromaticoligomer are primary amine(--NH₂), hydroxyl(--OH), carboxyl(--COOA whereA is hydrogen or an alkali metal), anhydride, thiol, secondary amine andepoxide groups. Especially preferred are reactive aromatic oligomershaving at least about 1.7 reactive groups per molecule and having atleast about 70% of the total number of reactive groups present asprimary amine, secondary amine, hydroxyl and/or epoxide groups.

The preferred reactive aromatic oligomers are made, for example, byreacting a molar excess of a sulfone such as dichlorodiphenylsulfonewith a dihydroxy aromatic compound or compounds such as bisphenol A or2,7 naphthalenediol so as to yield a chloro-terminated oligomer and thenreacting this chloro-terminated oligomer with an alkali metal salt of ahydroxy amine compound such as para or meta aminophenol to provide thereactive groups on the ends of the oligomer. Suitable sulfones for thisprocedure are meta, and para dichlorodiphenylsulfones. Among thesuitable dihydroxy aromatic compounds for use in this procedure arebisphenol A, bisphenol F, naphthalenediols and biphenyl diols. Otherprocedures for producing oligomers having reactive end groups aredisclosed in U.S. Pat. No. 3,895,064 to Brode and Kawakami and U.S. Pat.No. 3,563,951 to Radlman and Nischk, the latter patent using a procedurewhich involves forming nitro terminated oligomers and then reducing thenitro groups to amines.

An advantageous route for making the preferred amine terminated aromaticoligomers comprises: (a) dehydrating a dihydroxy aromatic compound or acombination of dihydroxy compounds with an amount of alkali metalhydroxide that provides slightly less than one equivalent of alkalimetal for each equivalent of hydroxyl in the dihydroxy compound orcombination thereof, the dehydration being in the presence of an organicliquid and an alkali metal carbonate in an amount which is at leastequivalent to the hydroxyl excess; (b) reacting a molar excess ofdihalogen diphenylsulfone bearing about two replacable halogens permolecule with the dehydrated product of (a) in the presence of anorganic solvent and an alkali metal carbonate; (c) dehydrating a phenolbearing epoxy-reactive functionality such as p-aminophenol,m-aminophenol or combinations thereof with alkali metal hydroxide in anamount that provides slightly less than one alkali metal equivalent foreach hydroxy equivalent in the aminophenol; and (d) reacting thedehydrated products of (c) with the condensed product of (b). Amineterminated polysulfone oligomers made in this manner have at least about70% of the end groups amine terminated and contain little or no organicchlorine substituents. Epoxide terminated aromatic oligomers can beprepared by the same route by reacting the condensed product of (b) or(d) with an amount of a polyepoxide compound sufficient to provide atleast one epoxide per equivalent of active hydrogen of (b) or (d).Preferably an excess of epoxide groups will be present and morepreferably the epoxide: hydrogen equivalence ratio will be between about5:1 and about 30:1. Generally the temperature of the reaction mixturewill be maintained at about 50° C. or above to ensure reaction in areasonable period of time. The preferred temperature range is about 80°to 150° C. Epoxide terminated polysulfone oligomers made in this mannercan contain up to 12 epoxide groups depending upon the epoxidefunctionality of the polyepoxide compound.

The glass transition temperature of the reactive aromatic oligomerpreferably ranges between 150° and 230° C. A more preferred range isbetween 160° and 190° C. The molecular weight (number average) of thereactive aromatic oligomer preferably ranges between 2500 and 5000.Preferably, the reactive aromatic oligomer has a polydispersity (M_(w)/M_(n) /M_(w)) of between about 2.0 and 4.0 where M_(n) is numberaverage molecular weight and M_(w) is weight average molecular weight.

The amine hardener of the thermosetting composition is preferably anaromatic diamine having a molecular weight below 750 and more preferablyis a compound of the formula ##STR3## where R₁, R₂, R₃ and R₄ areindependently hydrogen, halogen or an alkyl or alkoxy group with 1 to 12carbon atoms and X is O, S, SO₂ , alkylene, alkylidene, and oxoalkyleneand m is 0 or 1, a phenylene diamine or a heterocyclic diamine.Particularly preferred aromatic diamines are a diaminodiphenylsulfone; adiaminodiphenyl sulfide; a methylenedianiline such as4,4'-methylene-dianiline; a diaminodiphenylether; a diaminobenzophenone;benzidine; 4,4'thiodianiline; 4-methoxy-6-m-phenylenediamine;2,6-diaminopyridine; 2,4-toluenediamine; and dianisidine. Other aromaticdiamines such as the di(aminophenoxy)diphenyl ethers or sulfones can beemployed if desired. Alicylic amines such as menthane diamine may alsobe employed. In some cases aliphatic amines such as secondaryalkylamines which are normally fast reacting hardeners can be used aloneor in combination with other amine hardeners provided the concentrationand/or curing temperature are sufficiently low to permit control of thecuring rate. Other fast reacting hardeners which can be employed formaking the epoxy resins of the invention are dicyandiamide, borontrifluoride/amine complexes and the like.

The hardener is present in the composition in an amount sufficient tocrosslink or cure the composition into a thermoset and preferably ispresent in an amount which provides from 0.8 to 1.5 equivalents and morepreferably from 0.8 to 1.2 equivalents of active hydrogen atoms per oneequivalent of epoxide groups in the composition.

Table A below provides the general and preferred ranges, as weightpercent of the composition, for the polyepoxide component, reactivearomatic oligomer and hardener present in the thermosetting epoxy resincompositions of this invention:

                  TABLE A                                                         ______________________________________                                                      General                                                                              More Preferred                                           ______________________________________                                        Epoxide Component                                                                             25 to 60 30 to 55                                             Oligomer        20 to 50 25 to 45                                             Hardener        10 to 30 15 to 25                                             ______________________________________                                    

Other ingredients such as catalysts, modifiers, and the like can bepresent provided their presence and amount does not destroy theadvantages of the invention. For example, the inclusion of functionallyterminated elastomers such as carboxyl or amine terminatedbutadiene-acrylonitrile liquid rubbers can be added to improve peelstrength of the cured resins and composites thereof.

The cured, i.e., crosslinked resins produced from the compositions ofthis invention are characterized by a multiphase morphology comprisingat least one glassy discontinuous phase and at least one glassycontinuous phase. The domains of the dispersed discontinuous phasepreferably are between about 0.05 and 10 microns and more preferablybetween 0.1 and 5 microns in largest dimension. The domains aregenerally spherical or ellipsoidal in shape. The cured resins areinsoluble at room temperature in conventional solvents such as jet fuel,Skydrol hydraulic fuel, acetonitrile, acetone, tetrahydrofuran,dimethylsulfoxide, dimethylformamide, toluene, methylene chloride,methylethyl ketone (2-butanone), water and the like.

The volume of the discontinuous phases preferably constitutes at leastabout 30%, more preferably between 30% and 65% of the total volume ofthe cured resin. The total volume of the cured resin (Vr) is defined asthe volume of the continuous phase(s) (Vc) and the volume of thedisontinuous phase(s) (Vd) combined. In determining the volume of thediscontinuous phase(s), a micrograph of a microtomed section of thecured resin or composite is made and the area (or an area fraction) ofthe micrograph occupied by the continuous phase(s) (Ac), discontinuousphase(s) (Ad) and filament or fiber (Af) is determined visually orinstrumentally, using commercial devices such as a digitizer or imageanalyzer. The volume fraction or volume percent of the discontinuousphase is directly proportional to the area fraction or percent.Exceptionally tough multi-phase composites usually have discontinuousphases (Ad) comprising from about 45% to 55% of the total area of themicrograph less the area of the filaments (Ac+Ad-Af).

The preferred crosslinked resins are also characterized by a Tg of atleast 125° C. and a fracture toughness of at least 1.0 MPam^(1/2). Themost preferred crosslinked resins have a fracture toughness of 1.3MPam^(1/2) or greater and a cohesive fracture energy, G_(IC), of a least300 joules/meter². Addition of fiber does not affect the morphologicalcharacteristics of the cured resin (matrix) in the resulting thermosetcomposites. The preferred composites have a post impact compression atan impact energy of 1500 inch-pounds per inch thickness of at leastabout 35 and more preferably at least about 40 kilopounds per squareinch (ksi), as determined according to NASA publication 1092, using 32ply quasiisotropic laminates (4"×6"; (+45°/+90°/-45°/0° )_(4S)).

Thermosets of the compositions of this invention can be producedconventionally. Preferably the polyepoxide component and the reactivearomatic oligomer are first reacted together using an amount of thepolyepoxide component that ensures a resulting precursor having epoxidegroups and unreacted polyepoxide component, the hardener is added andcuring is completed. Alternatively, an admixture of the polyepoxidecomponent and an equivalent amount of the reactive oligomer can beprereacted and additional polyepoxide component added to form theprecursor--polyepoxide component mixture prior to the addition ofhardener and curing. If desired, the polyepoxide component, hardener andreactive aromatic oligomer can be admixed in bulk and cured to providethe thermosets of this invention.

Curing of the epoxy resin compositions of this invention usuallyrequires a temperature of at least about 40° C., up to about 200° C. ormore for periods of minutes up to hours. Post treatments can be used aswell, such post treatments ordinarily being at temperatures betweenabout 100° C. and 300° C. Preferably, curing is staged to preventexotherms, staging preferably commencing at temperatures below about180° C.

The cured epoxy resins are particularly useful in composites containinghigh strength filaments or fibers such as carbon (graphite), glass,boron and the like. Composites containing from about 30% to about 70%(preferably about 40% to 70%) of these fibers based on the total volumeof the composite are preferred in making composite structures.

A preferred manner of making the composites is by hot melt prepregging.The prepregging method is characterized by impregnating bands or fabricsof continuous fiber with the thermosetting epoxy resin composition inmolten form to yield a prepreg which is layed up and cured to provide acomposite of fiber and thermoset resin.

Generally, for hot melt processing it is preferred to select apolyepoxide component having a Tg below 20° C. and a reactive aromaticoligomer having amine or epoxide functional groups, which, when mixedtogether, provide a liquid epoxide functional precursor mixture having aviscosity of between about 10,000 and 100,000 centipoises (cps), morepreferably between 30,000 and about 70,000 cps at 100° C. In hot meltprepregging the combination of polyepoxide component, reactive aromaticoligomer and hardener preferably has a viscosity below 150,000 cps at100° C.

Other processing techniques can be used to form composites containingthe epoxy resin thermosets. For example, filament winding, solventprepregging and pultrusion are typical processing techniques in whichthe thermosetting epoxy resin composition can be used. Moreover, fibersin the form of bundles can be coated with the thermosetting epoxy resincomposition, layed up as by filament winding and cured to form thecomposites of this invention.

The cured epoxy resins and composites are particularly useful asadhesives and as structures for the aerospace industry and as circuitboards and the like for the electronics industry. Circuit boards requiregood adhesion to copper, dimensional stability, chemical resistance andhigh flexural modulus, all of which requirements are satisfied by thecompositions of this invention.

The following test procedures were employed in determining fractureenergies (G_(IC)) and critical stress intensity factors (K_(IC)) of thecured resins produced from the compositions of this invention. Themechanical strength of the cured (thermoset) resins was quantified interms of the mode I cohesive fracture energy, G_(IC) in joules/meter²(J/m²) or the mode I critical stress intensity factor, K_(IC) inmegapascals (MPa) times meters (m) to the one half power (MPam^(1/2)).The two are related through the following well known relationship whichmay be found in Fundamentals of Fracture Mechanics by J. F. Knott,Buttersworth, London (1973).

    K.sub.IC =(G.sub.IC E).sup.1/2

where E is Young's modulus, determined in accordance with ASTM D638.G_(IC) or K_(IC) can be quantified via numerous test methods such ascompact tension, double cantilever beam, double torsion and single edgenotch. The cured resins were tested herein using a single edge notchgeometry loaded in three point bending as described in Fracture ofEngineering Brittle Materials, Ayal de S. Jayatilaka, Applied SciencePublishers Ltd., London (1979). In carrying out the test, the resin wascast in the form of a 6 inch×7 inch×0.125 inch sheet which was thenmilled to yield a number of rectangular prisms, one of which is shown inFIG. 5(a) as prism 10, where L is 2.5 inches, w is 0.5 inch and t is0.125 inch. An edge crack 12 was made in each rectangular prism, specialcare being taken to insure that the crack plane was perpendicular to theprism's long axis. The crack length C_(L) was in the range of 0.12 inchto 0.22 inch, distances 1₁ and 1₂ each being one and one fourth (11/4)inch. Edge crack 12 was made by slicing the prism with a razor blade ata temperature about 40° C. above the resin Tg. Specifically, a prism ofthe above dimensions was fixedly clamped and passed over a stationaryrazor blade. The cutting edge of the blade was positioned in the prismthickness-width plane and at an oblique angle to the horizontal. Theclamped prism was placed in a large oven and conditioned for about 15minutes at a temperature about 40° C. above the thermoset's Tg. The edgecrack 12 was then made by passing the clamped prism over the stationaryrazor blade. The prism was then cooled to room temperature and placed inanother device which contained cavities similar in size to the prismdimensions. The device containing the cracked prism was placed in anoven and conditioned about 15 minutes at a temperature about 40° C.above the thermoset's Tg. The temperature was then decreased to about22° C. at a nominal rate of 1° C./min. The cracked specimens prepared asdiscussed above were then loaded in three point bending as shown in theFIG. 5(b) using an INSTRON® Model 1125 and tested at a crossheaddisplacement rate of 0.05 inch/min at a temperature of about 22° C.Crossbar 20 in FIG. 5(b) acted as the crosshead against stationarycrossbars 22 and 24 which were respectively distances 1₁ and 1₂ fromcrack 12. The distance 1₁ and 1₂ were each 2.54 centimeters. Distance Lwas 5.08 centimeters, t was 0.3175 centimeter and w was 1.27centimeters. At critical load, P_(c), the crack began to propagate andthe test was terminated. The following equation was used to calculate acritical stress intensity factor, K_(IC) : ##EQU1## where P_(c) is theload in newtons at which crack growth initiated; w is the width, 0.0127meter; L is the span, 0.0508 meters; t is the thickness, 0.003175meters; and c is the crack length, in meters.

Five (sometimes more) tests were made and the sample mean and standarddeviation determined. G_(IC) was then calculated using the previouslyshown relationship between G_(IC) and K_(IC). The modulus, E wascalculated from the shear storage modulus, G'(ω) assuming Poisson'sratio to be 0.35. G'(ω) was determined at ω=10 rad/sec and about 22° C.with a Rheometrics Mechanical Spectrometer and is reported ingigapascals (GPa).

To observe the glassy phases of the cured resins and composites preparedusing polysulfone oligomers, carbon fiber composite and neat cured resinsamples were thin sectioned at room temperature using a diamond knife.Thin sections (0.6-0.8 micron thick) were stained with RuO₄ vapor forfour minutes before being examined by a transmission electron microscopy(TEM) to determine morphology.

The procedure used for preparing the sections for transmission electronmicroscopy examination follows. A sample of the cured resin or compositecut to about a 2×2×10-mm size was placed in a metal chuck and attachedto a microtomer (LKB Ultratome V). The sample was prepared formicrotoming by first trimming the area to be thin sectioned into theform of a trapezoid using a glass knife. The trapezoidal shapedblockface was less than one millimeter in diameter. The glass knife wasreplaced with a diamond knife (Sorvall-DuPont) and the trough attachedto it was filled with distilled water. As the thin sections (600 to 800Angstroms) were cut, they were floated in a ribbon pattern on the watersurface. The sections were picked up using 300-mesh copper grids andallowed to air-dry. The grids containing the thin sections were attachedto a glass microscope slide and placed in a staining dish containing 2%aqueous RuO₄ (Aesar) for 4 minutes. The glass slide was removed from thestaining dish and the slide was placed under a hood to remove the lasttraces of any RuO₄. The stained microtomed sections were examined usinga Zeiss EM-10 transmission microscope at 60 KV and electronphotomicrographs were taken at 2000× and 5000×, and then enlarged to6000× and 15,000×, respectively.

The glass transition temperature, dry modulus, and wet modulus values ofneat cured resin and carbon fiber composite samples were obtained usinga Rheometrics Dynamic Spectrometer (RDS). All measurements were made inthe temperature sweep mode at a frequency of 10 rad/sec. The strainapplied to the torsional rectangular test samples (2.5"×0.5"×0.0125")was kept within 0.2% to insure that the measurements were in the linearviscoelastic range. The tan δ max temperature was defined as the glasstransition temperature (Tg) of the sample. Using the above procedures, adistinct Tg for each phase of the cured resin is not observed in thosecases where the separate phases have Tg's within about 15° C. of eachother.

The following examples illustrate this invention but are not meant aslimitations thereof. In these examples, unless otherwise specified, allparts and percentages are parts and percentages by weight. Molecularweight (M_(n)) values, as reported in the examples, were calculated fromend group analysis using the formula M_(n) =2000/meq, where meq=totalmilliequivalents of end groups by analyses, unless otherwise indicated.

EXAMPLE 1 Part A

To a 12 liter flask having a nitrogen inlet and equipped with athermometer, stirrer, condenser and Dean-Stark trap were added undernitrogen 1333 grams (5.8 moles) of bisphenol A, 1420 grams (11.3 moles)of a 44.8% aqueous potassium hydroxide solution and 160 grams of water.The contents of the flask were heated to 60° C. and maintained thereatfor 1/2 hour, at which time a homogeneous mixture was obtained. Next 960grams of toluene, 200 grams of potassium carbonate and 1900 grams ofdimethylsulfoxide were added to the flask and the contents were heatedto the reflux temperature (about 120° C.) to remove water as awater-toluene-dimethylsulfoxide azeotrope, 1200 grams of azeotrope beingcollected. The contents of the flask were cooled to 105° C., a solutionof 1887 grams (6.57 moles) of 4,4'-dichlorodiphenylsulfone in 2000 gramsof dimethylsulfoxide and 160 grams of toluene was added and theresulting mixture was heated to 160° C. and maintained at 160° C. for 16hours, toluene distillate being removed, as formed. The reaction mixturewas cooled to 120° C.

In a second flask a mixture of 159.4 grams (1.46 moles) ofp-aminophenol, 177.5 grams (1.42 moles) of 44.8% aqueous potassiumhydroxide solution, 60 grams of water, 240 grams of toluene and 900grams of dimethylsulfoxide was dehydrated at 120° C. for 4 hours. Thedehydrated mixture was transferred to the 12 liter flask under nitrogenand the resulting mixture was heated to 140° C. and maintained at 140°C. for 2 hours, following which time the reaction mixture was cooled toroom temperature. The cooled mixture was next filtered to remove thesolid inorganic salts and the filtrate was washed withdimethylsulfoxide. The washed filtrate (12 liters) was poured slowlyinto 48 liters of methanol to precipitate the p-aminophenol terminatedpolysulfone oligomer as a solid product. The precipitate was then washedwith water until free of chloride ions and the washed product was driedunder vacuum at 100° C. to give a yield of 94.7% amounting to 2746 gramsof oligomer having a melt viscosity (220° C.) of 11,000 poises, amolecular weight (M_(n)) of 4050 by size exclusion chromatography (SEC)and a glass transition temperature, Tg, of 175° C. End group analyses(OH=0.07meq/gram and NH₂ =0.28 meq/gram) indicated that greater than 74%of the end groups of the oligomer were amine terminated.

Part B

A vessel equipped with agitator and heating means was charged with 40parts of the p-aminophenol terminated polysulfone oligomer of Part A,above, and 40.8 parts of resorcinol diglycidyl ether (Heloxy 69 marketedby Wilmington Chemical Co.). The charge was heated to 100° C. andagitated for 1.5 hours, following which time 19.2 parts of4,4'-diaminodiphenylsulfone were added to the charge and agitation wascontinued for 10 minutes.

The vessel containing the charge was placed in a vacuum oven at 150° C.to remove entrapped air and then the mixture was poured into a preheated(177° C.) aluminum mold (cavity dimensions of 1/8"×6"×7"). The mixturewas cured in the mold for 2 hours at 177° C. followed by 2 hours at 200°C. under vacuum and then cooled to room temperature at a nominal rate of1° C./minute. The resulting cured resin was a thermoset having a glasstransition temperature, Tg, of 163° C. Mechanical property measurementsgave a calculated critical stress intensity factor, K_(IC) of 1.71±0.07MPam^(1/2), G'(ω) of 1.3 GPa and cohesive fracture energy, G_(IC), of833±68 joules/meter². Transmission electron micro RuO₄ -- stainedmicrotomed sections of the cured resin indicated a phase separatedmorphology consisting of a polysulfone oligomer rich continuous phaseand a discontinuous phase consisting of elliptical and circular shapeddomains of various sizes and having maximum dimensions in the range of0.5 micron to 4 microns. The discontinuous phase occupied about 55% ofthe area represented by the sections.

EXAMPLE 2

The procedure of Example 1, Part B was repeated with the exception thatthe charge contained 40 parts of the oligomer of Example 1, Part A, 21.5parts of resorcinol diglycidyl ether, 21.5 parts of diglycidyl ether ofbisphenol A (DER 332 marketed by Dow Chemical Co.) and 17 parts of4,4'-diaminodiphenylsulfone. The thermoset resin of this example had aTg of 185° C., a K_(IC) of 1.55±0.08 MPam^(1/2), G'(ω) of 1.32 GPa and aG_(IC) of 674±70 joules/meter². Transmission electron microscopy of RuO₄-- stained microtomed sections indicated a phase separation morphology.The continuous phase was rich in polysulfone oligomer and thediscontinuous phase consisted essentially of elliptical and circularshaped domains having maximum dimensions in the range of 0.5 to 3.5microns. About 50% of the area represented by the sections was occupiedby the discontinuous phase.

EXAMPLE 3

The procedure of Example 1, Part B was repeated except that the chargecontained 40 parts of the oligomer of Example 1, Part A, 21.6 parts ofresorcinol diglycidyl ether, 21.6 parts of diglycidyl ether ofbisphenol-F (Epiclon 830 marketed by Dainippon Ink and Chemicals) and16.8 parts of 4,4'-diaminodiphenylsulfone. The thermoset resin of thisexample had a Tg of 170° C., K_(IC) of 1.80±0.09 MPam^(1/2), G'(ω) of1.28 GPa and G_(IC) of 938±94 joules/m². The micrograph of RuO₄ --stained microtomed sections indicated a phase separated morphology, thediscontinuous phase of elliptical and circular shaped domains havingmaximum dimensions in the range of 1-5 microns and occupying about 55%of the area represented by the micrograph.

EXAMPLE 4

The procedure of Example 3 was repeated except that 21.6 parts of thetriglycidyl m-aminophenol (Epiclon EXA 4009 marketed by Dainippon Inkand Chemicals) was substituted for the 21.6 parts of the diglycidylether of bisphenol F. The thermoset resin had a Tg of 183° C., a K_(IC)of 1.86±0.05 MPam^(1/2), G'(ω) of 1.36 GPa and a G_(IC) of 986±53joules/meter². The micrograph of RuO₄ -- -stained microtomed sectionsindicated a phase separated morphology. The continuous phase was rich inpolysulfone oligomer and the discontinuous phase consisted of ellipticaland circular shaped domains having a size less than 3 microns. Thediscontinuous phase occupied about 50% of the area represented by themicrograph.

EXAMPLE 5

The procedure of Example 1, Part B was repeated except that the chargecontained 40 parts of the oligomer of Example 1, Part A, 20.8 parts ofresorcinol diglycidyl ether, 20.8 parts of N,N,N',N'-tetraglycidylmethylenedianiline (Araldite MY 720 marketed by Ciba-Geigy Corp.) and18.4 parts of 4,4'-diaminodiphenylsulfone. The thermoset resin of thisexample had a Tg of 195° C., a K_(IC) of 1.54±0.06 MPam^(1/2), G'(ω) of1.27 GPa and a G_(IC) of 692±54 joules/meter². The micrograph of RuO₄ --stained microtomed sections indicated a phase separated morphology. Thecontinuous phase was rich in the polysulfone oligomer and thediscontinuous phase consisted of elliptical and circular shaped domainshaving a size less than 3 microns. The discontinuous phase occupiedabout 50% of the area represented by the micrograph.

EXAMPLE 6

The procedure of Example 1, Part B was repeated except that the chargecontained 40 parts of the oligomer of Example 1, Part A, 20 parts ofresorcinol diglycidyl ether, 20 parts of triglycidyl p-aminophenol (CG0510 marketed by Ciba-Geigy Corp.) and 20 parts of4,4'-diaminodiphenylsulfone. The thermoset resin of this example had aTg of 188° C., a K_(IC) of 1.83±0.12 MPam^(1/2), G'(ω) of 1.34 GPa and aG_(IC) of 926±121 joules/meter². Transmission electron microscopy ofRuO₄ -- stained microtomed sections indicated a phase separatedmorphology. The continuous phase was rich in polysulfone oligomer andthe discontinuous phase consisted of elliptical and circular shapeddomains having a size less than 5 microns. The discontinuous phaseoccupied about 50% of the area represented by the sections.

EXAMPLE 7 Part A

The procedure of Example 1, Part A was repeated except that 1500 grams(6.57 moles) of bisphenol A and 2096.5 grams (7.3 moles) of4,4'-dichlorodiphenylsulfone were used and m-aminophenol was substitutedfor p-aminophenol. The m-aminophenol terminated polysulfone oligomericproduct (2372 grams; 74% yield) had a Tg of 173° C., a melt viscosity at220° C. of 3000 poises and a molecular weight (M_(n)) of 5100. End groupanalyses (OH=b 0.11 meq/g and NH₂ =0.28 meq/g) indicated that about 72%of the end groups of the oligomer were amine terminated.

Part B

The procedure of Example 1, Part B was repeated with the exceptions thatthe charge contained 40 parts of the oligomer of Part A, above, 38.5parts of resorcinol diglycidyl ether and 21.5 parts of4,4'-diaminodiphenylsulfone, air was removed in a vacuum oven at 180°C., and the aluminum mold was preheated to 180° C. The cured resin ofthis example was a thermoset having a Tg of 175° C., K_(IC) of 2.30±0.05MPam^(1/2), G'(ω) of 1.38 GPa and G_(IC) of 1420±62 joules/meter². Theresin was insoluble at room temperature in jet fuel, Skydrol hydraulicfluid, methylethyl ketone, methylene chloride and water. Transmissionelectron microscopy of RuO₄ -- stained microtomed sections of the curedresin indicated a two phase morphology. The continuous phase was rich inthe polysulfone oligomer and the discontinuous phase consisted ofelliptical and circular shaped domains having a size less than 5microns. The discontinuous phase occupied about 48% of the arearepresented by the sections.

EXAMPLE 8

The procedure of Example 1, Part B was repeated with the exceptions thatthe charge contained 40 parts of the oligomer of Example 7, Part A, 34.3parts of triglycidyl p-aminophenol (CG 0510 marketed by Ciba-GeigyCorp.) and 25.7 parts of 4,4'-diaminodiphenylsulfone, and air wasremoved in a vacuum oven at 140° C. The cured resin of this example wasa thermoset having two glass transition temperatures, Tg of 200° C. andTg of 267° C., K_(IC) of 1.75±0.05 MPam^(1/2), G'(ω) of 1.25 GPa andG_(IC) of 907±52 joules/meter². Transmission electron microscopy of RuO₄-- stained microtomed sections of the cured resin indicated a two phasemorphology. The continuous phase was rich in the polysulfone oligomerand the discontinuous phase consisted of elliptical and circular shapeddomains having a size between 0.5 micron and 3.0 microns. Thediscontinuous phase occupied about 45% of the area represented by thesections.

EXAMPLE 9

A vessel equipped with agitator and heating means was charged with 35parts of the oligomer of Example 7, Part A and 44.1 parts of resorcinoldiglycidyl ether. Agitation was commenced, the charge was heated at 130°C. for 1.5 hours and then cooled to 100° C. and 20.97 parts of3,3'-diaminodiphenylsulfone were added, agitation being continued at100° C. until dispersion appeared to be complete. The vessel was thenplaced in a vacuum oven at 180° C. to remove entrapped air, followingwhich the resulting resin was poured into a preheated (180° C.) aluminummold and the resin was cured for 2 hours at 177° C. followed by 2 hoursat 200° C. under vacuum. The cured resin was a thermoset having a Tg of180° C., K_(IC) of 2.19±0.02 MPam^(1/2), G'(ω) of 1.4 GPa and G_(IC) of1269±23 joules/meter.sup. 2. Transmission electron microscopy of RuO₄ --stained microtomed sections of the cured resin indicated a two phasemorphology. The continuous phase was rich in the oligomer and thediscontinuous phase consisted of elliptical and circular shaped domainshaving a maximum size less than 4 microns and occupying about 48% of thearea represented by the sections.

EXAMPLE 10 Part A

To a reaction flask equipped with thermometer, stirrer, Dean-Stark trapand condenser were added under nitrogen 71.3 grams (0.31 mole) ofbisphenol A, 50.5 grams (0.32 mole) of 2,7-dihydroxynaphthalene, 150grams of a 45% aqueous potassium hydroxide solution and 60 grams ofwater. Agitation was commenced and the contents of the flask were heatedto 60° C. for 1/2 hour, at which time a homogeneous mixture wasobtained.

Next 174 grams of toluene and 25 grams of potassium carbonate were addedto the reaction flask and the contents were heated at 90° C. until asolid mass was formed. Next 220 grams of dimethylsulfoxide were added tothe reaction flask and the contents heated to the boil to remove wateras a water-toluene-dimethylsulfoxide azeotrope. The reaction mass wascooled to 80° C. and a solution of 201.7 grams (0.7 mole) of4,4'-dichlorodiphenylsulfone in 220 grams of dimethylsulfoxide and 45grams of toluene was added to the flask. The reaction mass was heated to160° C. and maintained thereat for 16 hours, toluene being distilledfrom the mass and removed therefrom. The reaction mass was then cooledto 100° C.

Meanwhile, in a second flask a mixture of 17.03 grams (0.16 mole) ofm-aminophenol, 2 grams of potassium carbonate, 19.3 grams of 45% aqueouspotassium hydroxide solution, 20 grams of water and 110 grams ofdimethylsulfoxide was dehydrated by heating at 120° C. for 4 hours. Thedehydrated mixture was transferred to the reaction flask under nitrogenand the resulting mixture heated for 2 hours at 140° C., after whichtime the reaction mixture was cooled to room temperature and filtered toremove solid inorganic salts. The filtrate was washed withdimethylsulfoxide and the washed filtrate was slowly poured into 1 literof methanol to precipitate the m-aminophenol terminated polysulfoneoligomeric product. The product was washed free of chloride ions withwater and then dried under vacuum at 100° C. The product (192 grams, 66%yield) had a Tg of 186° C., and a molecular weight of about 5300. Endgroup analyses (OH=0.08 meq/g, NH₂ = 0.31 meq/g and Cl=less than 0.03meg/g), indicated that about 80% of the end groups of the oligomer wereamine terminated.

Part B

The procedure of Example 1, Part B was repeated except that the chargecontained 40 parts of the oligomeric product of Part A, above, 40.9parts of resorcinol diglycidyl ether and 19.1 parts of4,4'-diaminodiphenylsulfone. The cured resin was a thermoset having a Tgof 190° C., a K_(IC) of 1.74±0.07 MPam^(1/2), G'(ω) of 1.36 GPa and aG_(IC) of 863±69 joules/meter². The photomicrograph of a RuO₄ -- stainedmicrotomed section of the thermoset of this example is shown by FIG. 1.The photomicrograph indicates a two phase morphology. The dark (electrondense area) of FIG. 1 indicates that the continuous phase is rich inpolysulfone oligomer. The light area of FIG. 1 is the discontinuousphase and indicates that this phase consists of elliptical and circularshaped domains. The domains had a mean size of 0.74±0.16 micron and thediscontinuous phase occupied 50.5% of the area represented by thephotomicrograph.

EXAMPLE 11

The procedure of Example 10, Part B was repeated except that the chargecontained 35 parts of the oligomeric product, 44.1 parts of resorcinoldiglycidyl ether and 20.9 parts of 4,4'-diaminodiphenylsulfone. Thecured resin was a thermoset having a Tg of 180° C., a K_(IC) of1.69±0.05 MPam^(1/2), G'(ω) of 1.3 GPa and a G_(IC) of 814±48joules/meter². The photomicrograph of a RuO₄ -- stained section of thethermoset of this example is shown by FIG. 2 and indicates a two phasemorphology. The dark area of FIG. 2 indicates that the continuous phaseis rich in polysulfone oligomer and the light area indicates that thediscontinuous phase consists of elliptical and circular shaped domains.The domains had a mean size of 1.42±0.31 microns and the discontinuousphase occupied 47.8% of the area of the micrograph.

EXAMPLE 12

The procedure of Example 10, Part B was repeated except that the chargecontained 30 parts of the oligomeric product, 47.3 parts of resorcinoldiglycidyl ether and 22.7 parts of 4,4'-diaminodiphenylsulfone. Thecured resin was a thermoset having a Tg of 177° C., a K_(IC) of1.62±0.04 MPam^(1/2), G'(ω) of 1.2 GPa and a G_(IC) of 748±37joules/meter². The photomicrograph of a RuO₄ -- stained section of thethermoset of this example is shown by FIG. 3 and indicates a mixed phasemorphology. The dark areas of FIG. 3 indicate the phases which are richin polysulfone oligomer. The lower and central darkest area outlined inthe figure shows a continuous phase rich in polysulfone oligomer and adiscontinuous phase consisting of elliptical and circular shaped domainshaving a mean size of 0.92 micron. The discontinuous phase occupied35.9% of the darkest outlined area. The upper and lightest areas of thefigure show inverted phases, i.e., the discontinuous phase is rich inpolysulfone oligomer and consists of elliptical and circular shapeddomains having a mean size of 0.73 micron. The discontinuous phasesoccupied 14.7% of this area of the micrograph.

EXAMPLE 13

The procedure of Example 10, Part B was repeated except that the chargecontained 25 parts of the oligomeric product, 50.5 parts of resorcinoldiglycidyl ether and 24.5 parts of 4,4-diaminodiphenylsulfone. The curedresin was a thermoset having a Tg of 177° C., a K_(IC) of 1.34±0.07MPam^(1/2), G'(ω) of 1.3 GPa and a G_(IC) of 512±53 joules/meter². Thephotomicrograph of a RuO₄ -- stained section of the thermoset of thisexample is shown by FIG. 4 and indicates a two phase morphology. Thedark area of FIG. 4 indicates that the discontinuous phase consists ofelliptical and circular shaped domains which are rich in polysulfoneoligomer. The domains had a mean size of 1.16 microns and thediscontinuous phase occupied 17.3% of the area of the micrograph.

EXAMPLE 14 Part A

The procedure of Example 10, Part A was repeated except that 50 grams(0.27 mole) of biphenol was substituted for the 50.5 grams of2,7-dihydroxynaphthalene and 63.1 grams (0.27 mole) of bisphenol A,173.5 grams (0.60 mole) of 4,4'-dichlorodiphenylsulfone and 15 grams(0.14 mole) of m-aminophenol were used. The oligomeric product (231grams, 90% yield) was a m-aminophenol terminated polysulfone having a Tgof 181° C., a melt viscosity (220° C.) of 18,000 poises and a molecularweight of 3000. End group analyses (OH=0.07 meq/g and NH₂ =0.6 meq/g)indicated that about 89% of the end groups were amine terminated.

Part B

The procedure of Example 1, Part B, was repeated except that the chargecontained 40 parts of the oligomeric product of Part A, above, 38.6parts of resorcinol diglycidyl ether and 21.4 parts of4,4'-diaminodiphenylsulfone. The cured resin of this example was athermoset having a Tg of 180° C., a K_(IC) of 1.76±0.04 MPam^(1/2),G'(ω) of 1.32 GPa and a G_(IC) 869±40 joules/m². The micrograph of RuO₄-- stained microtomed sections indicated a two phase morphology. Thecontinuous phase was rich in polysulfone oligomer and the discontinuousphase consisted of eliptical and circular shaped domains having a sizeless than 5 microns. The discontinuous phase occupied about 45% of thearea represented by the micrograph.

EXAMPLE 15 Part A

To a reaction flask equipped with stirrer, thermometer, Dean-Stark trapand condenser were added under nitrogen 250 grams (1.1 mole) ofbisphenol A, 263.3 grams (2.12 mole) of 45% aqueous potassium hydroxide,50 grams of water, 220 grams of dimethylsulfoxide, 174 grams of tolueneand 30 grams of potassium carbonate and the mixture was dehydrated byheating at the reflux for 4 hours to remove water as awater-toluene-dimethylsulfoxide azeotrope. A solution of 279.5 grams(0.97 mole) of 4,4'-dichlorodiphenylsulfone in 220 grams ofdimethylsulfoxide and 43.5 grams of toluene was added to the reactionflask and the resulting mixture was heated to 160° C. and maintainedthereat for 16 hours, after which time 25 grams of acetic acid wereadded to the reaction mixture. The mixture was then poured slowly into 1liter of methanol to precipitate the product. The product was washedfree of chloride ions and the washed product dried under vacuum at 85°C. The product (420 grams) was a white powder having a melt viscosity(220° C.) of 15,000 poises, Tg of 180° C. and a molecular weight of3500. The oligomeric polysulfone product was hydroxyl terminated, basedon end group analyses (OH=0.57 meq/g).

Part B

A vessel equipped with nitrogen inlet, agitator and heating means wascharged with 30 parts of the oligomer of Part A, above, and 44.3 partsof resorcinol diglycidyl ether under nitrogen. Agitation was commenced,the charge was heated to 150° C., 0.74 part of triphenylphosphine(catalyst) was added and agitation was continued for 1 hour whilemaintaining a nitrogen atmosphere and a temperature of 150° C. Next thetemperature of the charge was reduced to 120° C., nitrogen flushing wasdiscontinued, 25 parts of 4,4'-diaminodiphenylsulfone were added and thereaction mixture was agitated for 5 minutes. The vessel was then placedin a vacuum oven at 180° C. to remove entrapped air from the resultingresin mixture, the resin mixture was poured into a preheated (180° C.)aluminum mold, the resin was cured for 2 hours at 180° C. followed by 2hours at 200° C. under vacuum and the cured resin was cooled to roomtemperature at a nominal rate of 1° C./minute. The cured resin was athermoset having a Tg of 160° C., K_(IC) of 1.76±0.05 MPam^(1/2), G'(ω)of 1.26 GPa and G_(IC) of 911±52 joules/meter². Transmission electronmicroscopy of RuO₄ -- stained microtomed sections of the cured resinindicated a phase separated morphology. The continuous phase was rich inpolysulfone oligomer and the discontinuous Phase consisted of ellipticaland circular shaped domains having a size less than 5 microns. Thediscontinuous phase occupied about 45% of the area of the sections.

EXAMPLE 16 Part A

The procedure of Example 15, Part A was repeated except that a solutionof 345.9 grams (1.2 moles) of 4,4'-dichlorodiphenylsulfone in 220 gramsof dimethylsulfoxide and 43.5 grams of toluene was used, and, followingheating of the resulting mixture to 160° C. for 16 hours, a sample ofthe reaction mixture was withdrawn and analyzed for OH content (OH=0.01meq/g). The reaction mixture was then cooled to 100° C., 54.4 grams(0.44 mole) of 45% aqueous potassium hydroxide were added and theproduct was heated to 125° C. and maintained thereat for 4 hours. Nextthe reaction mixture was poured slowly into 1 liter of methanol toprecipitate the oligomeric product, the precipitate was washed firstwith 1% aqueous hydrogen chloride and then with water and the washedproduct was dried under vacuum at 80° C. The product was a polysulfoneoligomer (399 grams, 70% yield) having a Tg of 180° C., a melt viscosityat 220° C. of 10,000 poises and an hydroxyl equivalency=0.47 meq/g.

Part B

The procedure of Example 15, Part B was repeated except that 35 parts ofthe oligomer of Part A, above were substituted for the 30 parts of theoligomer of Example 15, and 41.2 parts of resorcinol diglycidyl etherwere used. The cured resin of this example was a thermoset having a Tgof 176° C., K_(IC) of 1.24±0.05 MPam^(1/2), G'(ω) of 1.36 GPa and G_(IC)of 419±34 joules/meter². Transmission electron microscopy of RuO₄ --stained microtomed sections indicated a two phase morphology. Thecontinuous phase was rich in the polysulfone oligomer, and thediscontinuous phase consisted of elliptical and circular shaped domainshaving a size less than 5 microns. The discontinuous phase occupiedabout 40% of the area of the sections.

EXAMPLE 17 Part A

A first reactor equipped with temperature and pressure indicators,agitator, overhead condenser, separator and nitrogen purge was chargedwith 575 parts of dimethylsulfoxide and 135 parts of toluene. The chargewas sparged with nitrogen for 2 hours, following which time 117.5 partsof bisphenol A and 16.4 parts of potassium carbonate were added to thereactor with agitation. The reactor was inerted with nitrogen and thecontents of the reactor were heated to 40° C. Next, 124.2 parts of anitrogen-sparged, 45.13% aqueous potassium hydroxide solution were addedto the reactor and the contents were heated at the reflux temperature (atemperature range of 116°-140° C.) to remove water. During refluxing thesolvent system formed two layers in the separator. The upper layer(toluene rich) was returned to the reactor and the lower aqueous layerwas drained from the system. Refluxing was terminated when the reactionmixture contained 0.9% water, 246 parts of water and solvent having beenremoved, and the reaction mixture was cooled to 118° C.

To a second reactor containing 300 parts of nitrogen-sparged toluenewere added 162.7 parts of 4,4'-dichlorodiphenylsulfone, the reactor wasinerted and the contents were heated to 100° C. Next the contents ofthis reactor were transferred to the first reactor and the resultingmixture was heated to 160° C. and maintained at that temperature for 14hours, during which time toluene distillate was removed, as formed. Thereaction mixture was then cooled to 110° C.

A third reactor was charged with 120 parts of dimethylsulfoxide and 100parts of toluene and sparged with nitrogen for 10 hours. Next 11.2 partsof p-aminophenol and 2 parts of potassium carbonate were added to thereactor, the reactor was inerted with nitrogen , and 12.4 parts ofnitrogen-sparged 45.13% aqueous potassium hydroxide solution were addedto the reactor. The contents of the reactor were heated to the refluxtemperature (about 120° C.) and maintained at reflux to remove water, 59parts of water and solvent being removed. The dehydrated reactionmixture (containing 0.94% water) was cooled to 110° C. and transferredto the first reactor, and the resulting mixture was heated to 140° C.and maintained at 140° C. for 4.5 hours, following which time thereaction mixture was cooled to 130° C. Vacuum was next applied to remove75 parts of solvent (primarily toluene) from the system and theresulting mixture was cooled to 60° C. The cooled mixture was filteredto remove the solid inorganic salts, the reactor and filter cake wererinsed with dimethylsulfoxide, and the filtrate and rinsings werecollected and diluted to about 25% total solids with dimethylsulfoxide.A portion (about 100 parts) of the filtrate was poured slowly into avessel containing a mixture of 350 parts of methanol and 20 parts of a20% aqueous solution of sodium sulfite to precipitate the p-aminophenolterminated polysulfone oligomer as a solid product, the contents of thevessel were agitated for 0.5 hour and the contents were discharged fromthe vessel onto a filter. Remaining portions of the filtrate weretreated in the same manner until all of the product was collected on thefilter. The filter cake was first washed with water until free ofchloride ions and then with methanol and the washed product was driedunder vacuum at 100° C. The oligomeric product had a melt viscosity(220° C.) of 6200 poises, a molecular weight (M_(n)) of 4540 by sizeexclusion chromatography and a glass transition temperature, Tg, of 175°C. End group analyses (OH=0.02 meq/gram; NH₂ =0.36 meq/gram; and Cl=lessthan 0.03 meq/gram) indicated that about 90% of the end groups of theoligomer were amine terminated.

Part B

A vessel equipped with agitator and heating means was charged with 32.65parts of triglycidyl p-aminophenol (CG 0510) and 8.16 parts ofbutanediol diglycidyl ether (Araldite RD-2 marketed by Ciga-Geigy Corp.)and the charge was heated to 100° C. with agitation. Next 37.0 parts ofthe p-aminophenol terminated polysulfone oligomer of Part A, above, wereadded to the vessel and the resulting charge was maintained at 100° C.and agitated for 1.5 hours, following which time 22.19 parts of4,4'-diaminodiphenylsulfone were added to the charge and agitation wascontinued for 10 minutes.

The charge was transferred to an aluminum pan and cooled to roomtemperature. The pan containing the charge was Placed in a vacuum ovenand heated to 140° C. at a heating rate of 2° C./minute. When thetemperature reached 100° C., vacuum was applied to remove entrapped air.When the temperature reached 140° C., the vacuum was released and thecontents of the pan were transferred to a preheated (177° C.) aluminummold (cavity dimensions of 1/8"×6"×7"). The mixture was cured in themold for 4 hours at 177° C. and then cooled to room temperature at anominal rate of 1° C./minute. The resulting cured resin was a thermosethaving two glass transition temperatures, Tg of 190° C. and Tg of 229°C. Mechanical property measurements gave a calculated critical stressintensity factor, K_(IC) of 1.44±0.02 MPam^(1/2), (3 samples), G'(ω) of1.2 GPa and cohesive fracture energy, G_(IC), of 610±17 joules/meter².Transmission electronmicros copy of RuO₄ -- stained microtomed sectionsof the cured resin indicated a phase separated morphology consisting ofa polysulfone oligomer rich continuous phase and a discontinuous phaseconsisting of elliptical and circular shaped domains of various sizesand having maximum dimensions in the range of 0.5 micron to 2 microns.The discontinuous phase occupied about 50% of the area represented bythe sections.

EXAMPLE 18

The procedure of Example 17, Part B was repeated with the exceptionsthat the vessel was initially charged with 33.68 parts of triglycidylp-aminophenol and 8.42 parts of diglycidyl ether of polypropylene glycol(DER 736 marketed by Dow Chemical Co.) and 20.90 parts of4,4'-diaminodiphenylsulfone were used. The thermoset resin of thisexample had two glass transition temperatures, Tg of 185° C. and Tg of232° C., a K_(IC) of 1.47±0.03 MPam^(1/2), (3 samples), G'(ω) of 1.3 GPaand a G_(IC) of 636±26 joules/meter². Transmission electron microscopyof RuO₄ -- stained microtomed sections indicated a phase separationmorphology. The continuous Phase was rich in polysulfone oligomer andthe discontinuous phase consisted essentially of elliptical and circularshaped domains having maximum dimensions in the range of 0.5 to 2microns. About 50% of the area represented by the sections was occupiedby the discontinuous phase.

EXAMPLE 19 Part 1

A vessel equipped with agitator and heating means was charged with 40parts of the oligomeric product of Example 17, Part A and 38.5 parts ofresorcinol diglycidyl ether (Heloxy 69). The charge was heated to 100°C. and agitated for 1.5 hours, following which time the product wasrecovered, washed with acetone and dried. End group analyses for epoxidegroups (0.13 meq/gram), tertiary amine groups (0.06 meq/gram) and totalamine groups (0.24 meq/gram) indicated that about 22% of the end groupsof the oligomer were ePoxide terminated.

Part 2

The procedure of Part 1, above, was repeated except that followingheating the charge to 100° C. and agitating for 1.5 hours, 21.5 parts of4,4'-diaminodiphenylsulfone were added to the charge and agitation wascontinued for 10 minutes. The vessel was then placed in a vacuum oven at150° C. to remove entrapped air, the mixture was poured into a preheated(177° C.) mold and the mixture was cured in the mold for 2 hours at 177°C. followed by 2 hours at 200° C. under vacuum. The resulting curedresin was a thermoset having a calculated stress intensity factor,K_(IC), of 2.12±0.07 MPam^(1/2). The cured resin had a phase separatedmorphology consisting of a polysulfone oligomer rich continuous phase.

EXAMPLE 20 Part A

To a 12 liter reactor equipped with nitrogen inlet, thermometer,condenser and Dean-Stark trap were added 1141.5 grams (5.0 moles) ofbisphenol A, 1579.6 grams (5.5 moles) of 4,4'-dichlorodiphenylsulfone,5060 grams of dimethylsulfoxide, 871 grams of toluene and 760 grams (5.5moles) of potassium carbonate as a 30% aqueous solution. The reactor wasevacuated three times and then the contents were sparged with nitrogenand heated to 80° C., after which time 609 grams of toluene were added.The lower layer of the azeotrope which formed in the trap was removedand the reaction mixture was heated to 150° C. and maintained at 150° C.for 4 hours. Next 140 grams (1.0 mole) of potassium carbonate, 22 gramsof toluene and 220 grams of dimethylsulfoxide were added to the reactorand heating was continued for an additional 8 hours, the finaltemperature being 162° C. A sample, withdrawn from the reaction mixtureand precipitated in methanol gave, following washing and drying, a resinhaving a Tg of 173° C., a melt viscosity at 220° C. of 6000 poises andan hydroxyl equivalency of 0.01 meq/g.

In a second reaction vessel equipped with nitrogen inlet, stirrer,condenser and Dean-Stark trap a mixture of 110.2 grams (1.01 moles) ofp-aminophenol, 130 grams (1.01 moles) of 43.6% aqueous potassiumhydroxide solution, 130 grams of toluene and 630 grams (500 ml) oftetramethylene sulfone was dehydrated under nitrogen at 160° C. for 5hours. The dehydrated mixture was transferred to the 12 liter reactorthrough a cannula, the reactor contents having been cooled to 60° C.Toluene was removed from the Dean-Stark trap and the temperature of themixture was raised to 163° C. and maintained thereat for 2 hours,following which time the reaction was terminated. A 500 ml sample waswithdrawn from the reactor and poured into 5 liters of water containing100 grams of sodium hydroxide and 5 grams of sodium sulfite toprecipitate the resin. The precipitate was filtered, washed free ofchloride ions with water and dried. The dried product (105 grams) was apolysulfone oligomer having a Tg of 176° C. and a melt viscosity at 220°C. of 9000 poises, and gave on analysis, OH=0.05 meq/g, NH₂ =0.38 meq/gand Cl less than 0.03 meq/g. The remainder of the reaction product wasrecovered in the same manner as above and gave 1940 grams (80% yield) ofoligomer having a molecular weight (M_(n)) of 4762 by size exclusionchromatography.

Part B

The procedure of Example 1, Part B was repeated with the exception thatthe charge contained 35 parts of the oligomer of Part A, above, 41.58parts of resorcinol diglycidyl ether and 23.42 parts of4,4'-diaminodiphenylsulfone. The cured resin was a thermoset having aglass transition temperature of 176° C., K_(IC) of 2.01±0.07 MPam^(1/2),G_(IC) of 1134±79 joules/meter² and G'(ω) of 1.32 GPa. The micrograph ofRuO₄ -- stained microtomed sections indicated a two phase morphology.The continuous phase was rich in oligomer and the discontinuous phaseconsisted of elliptical and circular shaped domains having a size lessthan 5 microns. The discontinuous phase occupied about 40% of the arearepresented by the micrograph.

Part C

A resin matrix was prepared by heating with agitation a mixturecontaining 35 parts of the oligomer of Part A, above, and 41.58 parts ofresorcinol diglycidyl ether at 100° C. for 1 hour, cooling the mixtureto 80° C., adding 23.42 parts of 4,4'-diaminodiphenylsulfone andcontinuing agitation for 10 minutes.

The cooled matrix was applied to Hercules MAGNAMITE® AS6 carbon fibervia conventional prepregging techniques and 145 type (areal weight 145grams/meter²) tapes were made therefrom. Layers of the tapes wereassembled into laminates and cured via conventional bagmolding/autoclave techniques using a cure cycle of 2 hours at 177° C.followed by 2 hours at 200° C. under vacuum. The fiber volume was 57±2%of the volume of the laminate. Thirty two ply quasiisotropic laminates(4"×6";(+45°/+90°/-45°/0°)_(4s)) were tested for post impact compressionat several impact energies. The test procedure used is described in NASApublication 1092, modified as indicated above. Post impact compressionresults and other properties of composites formed from the tapes arereported in Table I below.

                  TABLE I                                                         ______________________________________                                        MECHANICAL PROPERTIES.sup.(1)                                                 Post Impact Compression                                                       Impact Energy (inch-lbs/inch thickness)                                                              ksi                                                    ______________________________________                                          0                    63.5 ± 1.1                                           500                   63.0 ± 0.4                                          1500                   46.1 ± 3.8                                          2500                   36.9 ± 3.3                                          Compressive Strength,  206 ± 15                                            (0°).sub.7 (ksi)                                                       Tensile Strength,      408 ± 28                                            (0°).sub.6 (ksi)                                                       Tensile Strain (%)      1.79 ± 0.03                                        Tensile Modulus (msi)  23 ± 1                                              ______________________________________                                         .sup.(1) Determined at 22.2° C.                                   

What we desire to protect by Letters Patent is:
 1. A method of making damage tolerant thermoset composites that comprise a crosslinked epoxy resin matrix and high strength filaments and retain substantial compressive strength after impact, said method comprising (a) combining said high strength filaments and an epoxy resin composition that separates into crosslinked glassy phases upon cure thereof, said epoxy resin composition comprising a crosslinkable oligomer that has a number average molecular weight between about 2,000 and about 10,000 and a glass transition temperature between about 125° C. and 250° C. and (b) curing of said epoxy resin in the presence of said filaments.
 2. The method in accordance with claim 1, wherein said crosslinkable oligomer comprises amine functionality.
 3. The method in accordance with claim 1, wherein said amine functional oligomer comprises a polyethersulfone unit.
 4. The method in accordance with claim 1, wherein said oligomer and an epoxy compound comprising at least one epoxy group on the average per molecule are admixed in forming said epoxy resin composition.
 5. The method in accordance with claim 1, wherein said epoxy resin composition comprises an amine hardener that is added to the admixture of said epoxy compound and said oligomer. 